1. Field of the Invention
The present invention relates to an optical apparatus having the combination of an image pickup optical system receptive of a light beam from an external field for forming an image on an image pickup element to produce image information and a display optical system for guiding a light beam representative of image information displayed on display means such as a liquid crystal display device to the eyeball of an observer, and more particularly to an optical apparatus suited to be used in instruments called the head-mounted display or glasses-type display.
2. Description of Related Art
It has been known to provide an instrument in which a small-sized CCD camera is added on the head-mounted display (HMD) and the image information obtained from the small-sized CCD camera is displayed in the HMD as it is, or an instrument in which the image information obtained from the small-sized CCD camera is converted by a processor into something of image information and this image information is displayed in the HMD. In the art of HMDs too, there have been many previous proposals for the see-through type of HMD (capable of directly observing light from the external field at unit angular magnification.)
Such a form of HMD has parallax produced when the line of sight or the optical axis of the display optical system for observing the image information on the display means of the HMD comes out of coincidence with the optical axis of the CCD camera for focusing light from the external field to form an image on the surface of the CCD and obtaining image information. Apparatus free from the parallax and having the combination of an image pickup optical system and a display optical system have been proposed in Japanese Laid-Open Patent Applications No. Hei 4-22358 and No. Hei 5-303053.
In the apparatus proposed in Japanese Laid-Open Patent Application No. Hei 4-22358, the display optical system is arranged such that a light beam emitted from a small-sized liquid crystal display panel is reflected by a mirror surface on one side of a plane mirror and, then, is guided to the eyeball of an observer through an eyepiece. Meanwhile, the image pickup optical system is arranged such that a light beam from the external field is reflected by a mirror surface on another side of the plane mirror and, then, is guided to a small-sized CCD camera to form an image thereon. However, since the flat mirror is disposed aslant at 45 degrees in the apparatus, the apparatus has a tendency to become large in size. In addition, since the eyepiece is disposed before the eyeball, a see-through optical system cannot be constituted.
In Japanese Laid-Open Patent Application No. Hei 5-303053, the construction having a see-through optical system is disclosed, but the structure of the construction is complicated. Therefore, the apparatus has a tendency to become very large in size.
Further, the technique related to the invention has been disclosed, for example, in U.S. Pat. No. 5,079,416, U.S. patent application Ser. No. 08/606,825, No. 08/607,125 and No. 08/606,824 each filed on Feb. 26, 1996.
In the art of HMDs or like instruments, because the observer has to bear the instrument on his or her head, the subject for reducing the size and weight of the whole instrument is of great importance. Also, there is demand for depriving the instrument of the parallax and reducing the bulk and size despite installation of the see-through optical system.